A short(ish) but clever tale for you:
A lunatic wanted to leave the asylum but was told he would first have to pass a test. He was given a calculator, paper and pen and told he had 2hrs.30mins to work out how many seconds there are in a year. Five minutes before time up he came back and said I've done it. There are 12 seconds in a year. He was asked how on earth he worked that out..........
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Well, he said, there's 2nd Jan, 2nd Feb, etc.....!